Fireworks are designed mainly to make a noise or to produce a beautiful sight. Early fireworks were noise-makers, and until about 100 years ago firecrackers formed the great majority of fireworks. Today display fireworks are the only kind in general use.
   Fireworks meant for display include the rocket, the Roman candle, the Bengal light, the fountain, the tourbillion, and combinations of these. Practically all are made in the same way. A tube of heavy cardboard is closed at one end, usually with clay, and filled with a mixture of gunpowder and coloring matter. Colors are produced by metal filings or salts, which burn with the gunpowder. If stars or fiery balls are desired, a paste of saltpeter, sulfur, charcoal, and coloring matter is cut into small pieces. Each of these explodes when the firework burns.
   The principle of the rocket is important in all moving fireworks. The burning of the gunpowder produces gases, which are inside the rocket under high pressure. Since these gases can escape from the rocket in only one direction, the rocket is pushed in the opposite direction.
   The pinwheel is simply a rocket fixed in a frame. The frame revolves around a nail or peg in its center. Since the rocket cannot sail into the air, it is forced to move in a circle around the peg.
   Set pieces, often large and complicated, include portraits, national flags or emblems, mottoes, and outlines of ships or airplanes. They are made by attaching small tubes of firework filler of different colors to strips of wood bent into the desired design.
   Fireworks have commercial and military uses. Anyone who has been on a highway at night has probably seen colored flares placed as warning signals around a stalled truck. Airplanes and ships carry rocket flares to use as distress signals in emergencies. Armies use flares for signaling and for lighting battlefields at night.